Project 1 Abstract The goals of Project 1 are to design and evaluate new versions of SOSIP trimers based on a range of HIV-1 genes with mutations to improve their structural, antigenic and immunogenic properties. The trimers designed in Project 1, with structure-based input from Project 2, are produced by Core B, provided to Project 2 for structural studies, assessed for antigenicity by Project 1, and sent to multiple collaborators for additional research, including animal immunogenicity studies. Project 1 will be closely involved in the overall scientific program. Dr. John P. Moore, will direct Project 1, at the Weill Cornell Medical College, New York. Dr. Rogier W. Sanders will lead a component at the Amsterdam University Medical Centers, Amsterdam. The Specific Aims are: Aim 1: To design Env trimers that can induce bNAb responses. We will design new and redesign existing SOSIP trimers by using high-resolution structures and animal immunogenicity data. We will create SOSIP trimer variants that target germline bNAb precursors (gl-bNAbs). We will further improve the overall SOSIP trimer ?recipe? for use with any given Env sequence, as trimers from multiple clades are likely to be necessary to steer NAb responses towards breadth. We will focus responses to bNAb epitopes on SOSIP trimers, by eliminating unwanted holes in glycan shields and by masking non-NAb epitopes that may act as decoys, including neo-epitopes on the trimer base. The overall goals are to better present mature-bNAb and gl-bNAb epitopes to the immune system, and drive Ab evolution toward bNAb development. Aim 2: To enhance the potency and durability of antibody responses by presenting SOSIP trimers particulate immunogens and incorporating T-helper epitopes. We will chemically couple SOSIP trimers to Iron Oxide nanoparticles (NP, 25-50 nm) to use as immunogens for priming antibody responses. To compensate for well-known deficiencies in endogenous Env-encoded T-cell helper epitopes, we will incorporate exogenous T-cell helper epitopes into the soluble and NP-presented SOSIP trimers. The overall goals are to overcome limitations to the immunogenicity of HIV-1 Env proteins in general. Aim 3: To design and evaluate animal immunogenicity studies using SOSIP trimers. Our team has well-established collaborations with several groups as well as access to other non-NIH funding support that together enable it to conduct animal immunization studies that are not directly paid for by this award. Project 1 will work with collaborators to design immunogenicity experiments and contribute to the analysis and interpretation of these studies by performing neutralization, NAb-epitope mapping and related serology assays. The overall goals are to further advance the design of SOSIP trimers and trimer-based vaccination regimens that are capable of inducing bNAbs.